Speed (t)RacerGene Au-yeung, Daniel Quach, Jeffrey Su, Albert Wang, Jessica Wang, David Woo

What Is Ray Tracing?

Rendering technique: 3D scene to 2D image

Simulates physics of light propagation (rays).

Primary ray: from perspective of viewer (shot for every pixel on the screen)

Algorithm determines which object is hit first on ray’s path

What Is Ray Tracing? (cont’d)

At that hitpoint, a shader program is invoked.

To simulate a mirror reflection, the shader program can cast another ray

What Is Ray Tracing? (cont’d)

Shadow rays depend if the pixel is lit or in shadow

A pixel is lit if a ray can be shot to the light source without obstruction

If blocked, the pixel is in shadow

Sequential Algorithm

for each row for each column▪ Construct ray from camera through

pixel (row, column)▪ Find first shape hit by ray▪ If (shape)

Calculate color at intersection point▪ Else

Calculate background color▪ Draw color

Sequential Algorithm

Color Calculation for each light source▪ if light is visible from this point▪ Add light source’s contribution

Add contribution due to reflected ray

Add contribution due to refracted ray

Raytracer Features

Currently supports: spheres, reflections, shadows, diffuse lighting

Implement: Refraction (Gene) Planes (David) Triangles (Albert) Textures (Jessica) Anti-Aliasing (Gene, Daniel)

Parallelization: Initial investigation: Jeffrey Whoever finishes their feature help Jeffrey

Anti-Aliasing

Parallelization Opportunities

The bulk of ray tracer’s work lies in the recursive steps of reflecting each ray

However, we cannot parallelize each reflection since the second reflection cannot be completed until the first is doneMust wait for this ray to

trace

Before starting the 2nd or 3rd

Parallelization Opportunities

Instead, we can parallelize the primary rays traced from the camera to the viewport

Divide viewport into 8 columns, have one thread calculating primary rays in each column

No data dependency, since each pixel’s color can be found independently of other pixels

Parallelization Opportunities

With addition of anti-aliasing, a potential data dependency can occur as each primary ray requires information about the results of surrounding rays

Our potential solution is to re-check for edges at the boundaries between the 8 columns, then only apply anti-aliasing to pixels which are an edge

Projected Schedule

Currently: framework and repository ready

Week 7: Implement raytracing features Investigate parallelism using baseline

code Week 8:

Parallelize finished raytracer Week 9:

Conduct performance tests between sequential and parallelized versions

Sources

http://www.athlonmp.com/reviews/processors/ray-tracing-and-gaming-one-year-later/

http://www.codermind.com/articles/Raytracer-in-C++-Part-III-Textures.html